Electronic thermometers employing thermistors as transducers are known in the prior art. One major limitation of these thermometers, however, is that they are limited to a relatively confined range of accurate temperature measurement. This limited range of accurate temperature measurement is not always suitable for all clinical and medical uses since there are situations where temperatures outside of the limited accurate range must be measured or checked. For example, one such situation is measuring the temperature of premature babies who typically have temperatures much lower than the normal temperature range of a human being.
The limitation to a relatively confined range of accurate temperature measurement results in significant part because the resistance characteristic of the thermistor is not linear over the temperature range of the thermistor. Consequently, in the prior art it has been necessary to chose a small portion of the resistance-temperature relationship curve of the thermistor and linearize that portion for use in calculating the temperature. Linearizating a portion of the resistance-temperature relation curve has had the effect of limiting the usable range of accuracy to about 12 degrees Fahrenheit. To avoid inaccurate temperature measurements, some prior art clinical thermometers are operative to suppress all temperatures outside of this predetermined range of accuracy. Other prior art electronic thermometers will provide information of the temperature outside of the given range of accuracy, but the user must specifically understand and appreciate that the temperature measurement is not accurate except within the predetermined range of accuracy. Thus in the prior art, either no temperature measurement is provided outside of a limited range, or the temperature measurement provided is possibly not accurate and requires the user's recognition of the potential for nonaccuracy. Neither situation is satisfactory, particularly in medical uses where accuracy and freedom from mistake can be of critical importance.
The limitations of prior art electronic thermometers are also apparent in applications other than those of a medical or clinical nature. Many industrial, laboratory, scientific, manufacturing and home situations require accurate measurements within wide temperature ranges of up to 200 degrees, for example. It is apparent that prior art electronic thermometers are not typically capable of providing accurate measurements over wide ranges.
One cause for the inability of prior art electronic thermometers to provide accurate measurements over wide temperature ranges has been the inability to accurately simulate or approximate the nonlinear response characteristics of the thermistor in a manner which can be conveniently employed to calculate temperature.
Other limitations and disadvantages of prior art electronic thermometers are known and appreciated, and limited solutions to some of these problems may have been achieved. In general, however, the various factors, problems, limitations and disadvantages present in the prior art should become more fully recognized and appreciated in light of the improvements and teachings of the present invention.